Graphics displays have become prominent in the computer graphics visual technologies and commonplace for the projection of variegated displays, from letters and words and to extremely intricate technical drawings and data. Some of the components currently used to produce such images are: cathode ray tubes, light-emitting diodes, liquid-crystal electroluminescence devices, and devices utilizing magnetic-particle, plasma, electrochromic, and dye-foil.
The display area of a graphics display generally incorporates an abundance of horizontal and vertical lines of pixels comprising a Cartesian coordinate system. The word pixel originates from the words "picture element" because the pixels, when energized, form the picture seen in the graphics display. Since each pixel is at the intersection of horizontal and vertical lines of pixels, each represents a point that is addressable using Cartesian coordinates. Therefore, each pixel is known as an addressable point.
Therefore, the image produced on a graphics display consists of a series of pixels that have been addressed by a computer to produce a visual display of a specific image. The computer, in turn, receives its commands either from hand or electronic tabulation, such as programming, or directly from an electro-mechanical apparatus, such as is described below relative to this invention, or a combination of both.
In current practice it is common to use digitizers to convert coordinate information into computer-acceptable form for transfer into a graphics display. Some digitizers utilize horizontal and vertical printed circuit wires embedded beneath a flat surface. Electrical induction of coordinates, in such systems, is induced by a wire-wound cursor element. The coordinates, which represent an addressable point, are usually determined with a microprocessor and conducted to a computer. It is obvious that working directly upon a graphics display is not possible with this configuration, since effort must be performed separately on a special printed circuit table while intermittently viewing the graphics display. With such a system the location of coordinates, other than on a surface directly backed with a printed circuit, is not possible.
Another conventional digitizing technique employs a "light-pen," an electronically induced pen-like instrument that must be placed directly upon the display. It emits a light, or spot, within the display area at the "light-pen" point of contact. Contrary to the above-described "printed-circuit" practice, the "light-pen" technique is limied only to the graphics display area. A computer program is then designed to determine the coordinates of the light spot emitted so that its location can be signaled to the computer. The "light-pen" technique cannot be utilized to determined coordinate points on such as a drawing positioned on a table and to transfer these to a graphics display.
Still another digitizer method uses a horizontal arm attached to the upper edge of a table. A vertical arm, coupled with and movable along the horizontal arm, travels from side to side over the surface of the table. The vertical arm contains a stylus-like instrument which, when placed upon a point and a corresponding button is depressed to complete the circuit, causes a computer to determine the x-y coordinates of the point. It may be visualized that the use of this system is extremely restrictive; i.e., to a specific table designed to accept the arm members which support the device containing the stylus.